Ion Partitioning Research Articles

Ionic Conductivity, Salt Partitioning, and Phase Separation in High-Dielectric Contrast Polyether Blends and Block Polymer Electrolytes

Ionic Conductivity, Salt Partitioning, and Phase Separation in High-Dielectric Contrast Polyether Blends and Block Polymer Electrolytes

Response Mechanism of Polymeric Liquid Junction-Free Reference Electrodes Based on Organic Electrolytes.

To achieve a transition from conventional liquid-junction reference electrodes (LJF REs) to their all-solid-state alternatives, organic electrolytes are often introduced into the polymeric electrode membranes. In this article, we implement a theoretical approach to the explanation and quantification of the boundary potential stabilization phenomenon for the electrodes modified with organic electrolytes (Q+B-). For the first time, stabilization of the phase boundary potential due to the partition of lipophilic ions of the Q+B- electrolyte between the polymeric and aqueous phases is numerically simulated to predict the LJF electrodes behavior. The impact of the hydrophilic electrolyte on the potential stabilization is demonstrated both numerically and experimentally. The developed model predicted that the small additions of a traditional ion-exchanger enhance performance of the Q+B--based reference electrodes. For some specific cases, the optimal concentrations of Q+B- and ion-exchanger in the polymeric phase are suggested to provide stable electrode potential in a broad range of aqueous electrolyte concentrations. In addition, the efficiency of the stabilization was shown to be dependent on the overall Q+B- load in the polymeric membrane rather than on the closeness of the partition coefficients of the Q+ and B- ions; and on the volume of the aqueous phase. The model results are verified experimentally with poly(vinyl chloride) membranes containing ion-exchanger or hydrophilic electrolyte and Q+B- in various proportions. A good agreement between the measured electrode response and the theoretical results is observed in a broad range of solution concentrations. In particular, the cationic function of membranes containing KTpClPB is suppressed, and the electrodes begin to behave as REs starting from 50-60 mol. % of ETH500 electrolyte added to the membrane, relative to the total amount of salt.

Gating ion and fluid transport with chiral solvent.

The development of modern membranes for ionic separations and energy-storage devices such as supercapacitors depends on the description of ions at solid interfaces, as is often provided by the electrical double layer (EDL) model. The classical EDL model ignores, however, important factors such as possible spatial organization of solvent at the interface and the influence of the solvent on the spatial dependence of the electrochemical potential; these effects in turn govern electrokinetic phenomena. Here we provide a molecular-level understanding of how solvent structure can dictate ionic distributions at interfaces using a model system of a polar, aprotic solvent, propylene carbonate, in its enantiomerically pure and racemic forms, at a silica interface. We link the interfacial structure to the tuning of ionic and fluid transport by the chirality of the solvent and the salt concentration. The results of nonlinear spectroscopic experiments and electrochemical measurements suggest that the solvent exhibits lipid-bilayer-like interfacial organization, with a structure that is dependent on the solvent chirality. The racemic form creates highly ordered layered structure that dictates local ionic concentrations, such that the effective surface potential becomes positive in a wide range of electrolyte concentrations. The enantiomerically pure form exhibits weaker ordering at the silica surface, which leads to a lower effective surface charge induced by ions partitioning into the layered structure. The surface charge in silicon nitride and polymer pores is probed through the direction of electroosmosis that the surface charges induce. Our findings add a new dimension to the nascent field of chiral electrochemistry, and emphasize the importance of including solvent molecules in descriptions of solid-liquid interfaces.

The effect of monomer polarizability on the stability and salt partitioning in model coacervates.

Coacervation of charged polymer chains has been a topic of major interest in both polymer and biological sciences, as it is a subset of a phenomenon called liquid-liquid phase separation (LLPS). In this process the polymer-rich phase separates from the polymer-lean supernatant while still maintaining its liquid-like properties. LLPS has been shown to play a crucial role in cellular homeostasis by driving the formation of membraneless organelles. It also has the potential to be harnessed to aid in novel therapeutical applications. Recent studies have demonstrated that there is no one simple mechanism which drives LLPS, which is instead a result of the combined effect of electrostatic, dipolar, hydrophobic, and other weak interactions. Using coarse-grained polymer simulations we investigate the relatively unexplored effects of monomer polarizability and spatially varying dielectric constant on LLPS propensity, and these factors affect the properties of the resulting condensates. In order to produce spatial variations in the dielectric constant, all our simulations include explicit solvent and counterions. We demonstrate that polarizability has only a minor effect on the bulk behaviour of the condensates but plays a major role when ion partitioning and microstructure are considered. We observe that the major contribution comes from the nature of the neutral blocks as endowing them with an induced dipole changes their character from hydrophobic to hydrophilic. We hypothesize that the results of this work can aid in guiding future studies concerned with LLPS by providing a general framework and by highlighting important factors which influence LLPS.

Smart nanochannels: tailoring ion transport properties through variation in nanochannel geometry.

This research explores ion transport behavior and functionality in a hybrid nanochannel that consists of two conical and cylindrical parts. The numerical investigation focuses on analyzing the length of each part in the nanochannel. The nanochannels are hybrid cavities embedded in a membrane, where the size of the conical part varies as equal to, larger than, or smaller than the cylindrical part. The nanochannel is coated with a polyelectrolyte layer that exhibits a dense charge density distribution. The charge density of the soft layer is described using the soft step distribution function. We study the electroosmotic flow, ionic current, rectification, and selectivity of the nanochannel versus bulk electrolyte concentration, the charge density of the polyelectrolyte layer, and decay length, while considering the effect of ionic partitioning. The steady-state Poisson-Nernst-Planck and Navier-Stokes equations are solved using the finite element method. The findings reveal that the nanochannel with a more extensive conical section demonstrates increased rectification, with the rectification factor rising from 1.4 to 2 at a bulk concentration of 100 mM. Additionally, the nanochannel with a longer cylindrical part exhibits improved selectivity under negative voltage conditions, while positive voltage introduces a different situation. The nanochannel with equal cylindrical and conical parts significantly affects conductivity by modifying the charge density in the soft layer, resulting in a 3.125-fold increase in conductivity under positive voltage when the charge density in the polyelectrolyte layer is raised from 25 to 100 mol m-3. This research focuses on creating intelligent nanochannels by controlling mass concentration, charge density, and collapse length, improving system performance, and optimizing properties. It also offers valuable insights into ion transport mechanisms in nanochannel systems, advancing our understanding in this field.

Impact of hydrodynamics and rheology of the ion partitioning effect on electrokinetic flow through a soft annulus with a retentive and absorptive wall.

The theoretical analysis for the mass transfer process of an oscillatory electroosmotic flow (EOF) in the fractional Jeffrey fluid model is studied through a polyelectrolyte layer (PEL) coated cylindrical annulus with reversible and irreversible wall reactions. The ion partitioning effect is observed due to the difference in permittivity of the PEL and the electrolyte solution, which is accounted for by the Born energy. Considering ion partitioning effects, analytical solutions for induced potential and axial velocity are presented, respectively in both the PEL and electrolyte region from the modified Poisson-Boltzmann equation and the Cauchy momentum equation with a proper constitutive equation, respectively. The Maxwell fluid and classical viscous Newtonian fluid models can be achieved separately by adjusting the relaxation and retardation time in the constitutive equation of this model. The analytical solution of the convection-diffusion equation for solute transport is established in the full domain. The separation of species is found to be dependent mainly on the Damköhler number, absorption parameter, phase partitioning coefficient, etc. It is observed that the osmotic pressure increases with the thickness and fixed charge density of the PEL. The velocity decreases with an increase in the permittivity difference of these layers. Our results suggest that the separation may be achieved through a difference in absorption kinetics.

Boost ionic selectivity by coating bullet-shaped nanochannels with dense polyelectrolyte brushes

The influence of channel geometry on the ionic selectivity and ionic current rectification of soft nanochannels was numerically investigated. The nanochannels coated with polyelectrolyte layers (PELs) are termed as soft nanochannels. The asymmetric category of nanochannels, i.e., bullet-shaped, was considered in this study. When PEL is dense, the ionic partitioning effect cannot be ignored. To this end, through adopting a numerical approach using the finite element method, Poisson–Nernst–Planck and Navier–Stokes equations were solved at steady-state conditions by considering different values of permittivity, diffusivity, and dynamic viscosity for the PEL and the electrolyte. The results show that the PEL–electrolyte property difference leads to a significant improvement of the rectification behavior, especially at low and moderate salt concentrations. This not only highlights the importance of considering different properties for the PEL and the electrolyte but also implies that the rectification behavior of soft nanochannels/nanopores may be improved considerably by utilizing denser PELs. Considering a charge density of 80 mol/m3 and a bulk concentration of 20 mM, we demonstrate that the rectification factors for the bullet nanochannels, from 3.35 by ignoring the ion partitioning effect, can reach the values of 4.88 by considering the ion partitioning effect, respectively.

Impact of Ion Partitioning Effect on the Electroosmotic Flow of Non-Newtonian Fluid and Ion Selectivity through Soft Nanochannel

Impact of Ion Partitioning Effect on the Electroosmotic Flow of Non-Newtonian Fluid and Ion Selectivity through Soft Nanochannel

Simulations Explain the Swelling Behavior of Hydrogels with Alternating Neutral and Weakly Acidic Blocks

We used computer simulations to study the equilibrium swelling of weak (pH-responsive) polyelectrolyte hydrogels as a function of pH and salt concentration in a supernatant solution. Our simulations were designed to represent recently synthesized gels composed of tetrapoly(acrylic acid) and tetrapoly(ethylene glycol) stars. To model the ionization equilibrium of the weak acid groups and the exchange of small ions with the reservoir, we applied the recently developed grand-reaction Monte Carlo method. We showed that the ionization of these gels as a function of the pH significantly deviates from the ideal Henderson–Hasselbalch equation due to two main contributions: (1) electrostatic interactions and (2) Donnan partitioning of small ions. The first contribution dominates in the gels composed of alternating neutral and acidic blocks, contrasting with our previous observations that both contributions are comparably strong in hydrogels composed of homogeneously distributed weak acid groups. We also critically examined the counterion condensation argument, previously invoked to explain why the experimentally observed swelling was lower than predicted by theory. Thus, a detailed analysis of the simulations allowed us to understand which of the above effects dominates in different systems and why, thereby allowing us to identify the correct physical origin of the deviations from ideal swelling. Such an understanding is important not only for correctly interpreting experimental measurements but also for designing polyelectrolyte gels tailored to exhibit specific swelling response to pH and salt concentration.

Quantifying the coupled monovalent and divalent ions sorption in dense ion-exchange membranes

As a universal phenomenon in solution-membrane systems, the coupled competitive monovalent and divalent ions sorption significantly impacts the transport process in ion-exchange membranes. Often, the quantitative and qualitative relationships between them are unclear. Here, we present a lattice-based molecular model to capture the interplay effect of ion-pairing and electrostatic interaction on the competitive partitioning process. In particular, we utilize statistical mechanics to formulate how the monovalent and divalent counterions competitively pair with the fixed charge group in the membranes. To this end, the model can quantify (a) the counterions sorption and (b) the coion repulsion within the membranes, which, collectively, allow us to quantify the ion partitioning and the pairing site saturation. To showcase the capability of our model, we compare our results with published experiment data, where we achieve a relatively good agreement between them. We demonstrate that the competitive ion partitioning depends highly upon (i) the entropy change generated by the counterions pairing with the fixed charge group, (ii) the binding energy, and (iii) the osmotic pressure, and (iv) the electrostatic interaction. These different factors can explain the favorable sorption of divalent counterions in the cation-exchange membranes but monovalent counterions in the anion ones, as previously reported. Altogether, our theoretical approach provides an insight into the fundamental understanding of coupled competitive monovalent and divalent ions sorption within the dense ion-exchange membranes, further enhancing the knowledge of the competitive ion partitioning process.

Electrophoresis of a soft particle with a hydrophobic rigid core decorated with a soft-step and partially ion-penetrable polymer layer

On the basis of flat-plate formalism, we present an analytical theory for the electrophoresis of soft particles consisting of a hydrophobic inner core decorated with a layer of inhomogeneously distributed polymer segments. Biocolloids or bio-compatible drug delivery vehicles often carry the non-wettable or hydrophobic inner core. In addition, due to electrostatic swelling/shrinking processes, a spatially varying heterogeneity can be seen in the monomer distribution as well as charge properties of the peripheral polyelectrolyte layer (PEL). We adopt the soft-step function to model the chemical and structural anisotropy of the peripheral PEL. In addition, the PEL for the aforementioned bio-systems immersed in aquatic microenvironment often induces dielectric gradient-mediated ion partitioning effect, which in turn leads to the PEL to be partially ion penetrable. Within the Debye–Hückel electrostatic framework, we derive a general expression for electrophoretic mobility of a soft particle considering the combined impacts of hydrophobicity of the inner core, inhomogeneously distributed segment distribution accompanied by chemical heterogeneity and ion partitioning effect. We further derived asymptotic limits of the more generic results detailed here under several electrostatic and hydrodynamic conditions.

Chemically Sensitive Field‐Effect Transistors, Past, Present and Future

AbstractHistory, failures, successes and potential of Chemically Sensitive Field Effect Transistors (CHEMFET) are presented, based on fifty years of Author's personal experience working in this field. This article is divided into operation of devices in the liquid phase and in the gas phase. The recognition step in the first is based on ion partitioning. It requires a macroscopic reference electrode, which becomes the principal limiting factor. The CHEMFETs for dry operation rely on selective chemical modulation of work function of the electronically conducting gate material. They do not require an external reference and offer the possibility of miniaturization and multivariate sensing. Fabrication and economic aspects of both types of CHEMFETs are also discussed.

Transparent Eu3+ doped oxyapatite glass ceramics: Crystallization kinetics, structural and optical properties

Transparent Eu3+-doped oxyapatite glass ceramics (GC) have been prepared. A mean crystallization activation energy of 389.58 kJ/mol is determined in crystallization kinetics study. The Avrami's parameter is evaluated to be 2.65, indicating that bulk crystallization is the dominant mechanism. Effect of Eu2O3 dopant on the crystallization behavior was discussed. The precipitation of oxyapatite nanocrystals exhibiting a slight lattice contraction in glass is confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements, resulting from the partition of some europium ions into crystals. Photoluminescence analysis reveals that crystallization could promote the oxidation of Eu2+ to Eu3+ possibly due to europium ions partition on La3+ lattice sites. Temperature-dependent photoluminescence spectra indicate that such oxyapatite GC phosphor exhibits excellent thermal stability with an activation energy of 0.326 eV. This study reports the possibility of developing oxyapatite GC phosphor for light conversion application.

Importance of nanochannels shape on blue energy generation in soft nanochannels

Energy production is one of today's most pressing issues. Finding alternative energy sources has become one of the hottest research areas for scholars due to the limited use of fossil resources. Using water sources of different concentrations is one of the newest methods of energy production. Due to the energy of mixing fluids, two fluids of different concentrations on both sides of a nanochannel membrane can produce energy. Given the costs and restrictions of studying complex systems experimentally, simulation is required to investigate their behavior and determine the best states. As a result, using an energy production strategy, this work explores the effect of nanochannel shape on the ion transfer behavior. Asymmetric (bullet, trumpet, cigarette, hourglass, and hill) and symmetric (cylindrical) geometries were utilized. The effects of different geometries, soft layer density, and concentration ratio on energy production considering the effect of ion partitioning in soft surfaces was investigated. A finite element numerical computation approach was employed to solve the Poisson-Nernst-Planck and Navier-Stokes equations at steady-state. The best geometry at various concentration ratios to create the most performance were: cylindrical and cigarette for osmotic current, hourglass and trumpet for transmission number, hourglass and trumpet for diffusion potential, cylindrical for electrical conductivity, cylindrical and trumpet for power capacity, and hourglass and trumpet for energy conversion efficiency, respectively. In the case of considering the ion partitioning at a concentration ratio of CH/CL=1000for trumpet geometry, raising the soft layer's charge density from NPEL/NA=25to100mol/m3 boosted the maximum produced power by about 25 times, from 0.215pW to 5.35pW.

Investigate the equivalent weight effect on properties of perfluorosulfonic acid membrane in concentrated electrolytes

In this contribution, a series of characterizations, such as water uptake, acid uptake, membrane density, and conductivity measurements, have been utilized to study the effect of equivalent weights (EW) on ion partitioning and transport behavior of perfluorosulfonic acid membranes produced by 3M Corp. It is observed that water sorption and acid uptake both increase with a decrease in EW. This phenomenon results from a higher sulfonic acid site density in the membrane with a lower EW. Just as important, the Donnan potential opposing co-ion uptake on the membrane surface decreases with decreasing equivalent weight. The membrane with a lower EW is found to have a higher membrane density at the same water content, but the porosity does not show a large discrepancy among the three membranes we studied. Even though the higher acid concentration in membranes results in lower activity coefficients of ions, its higher water content still facilitates faster proton mobility and higher ion conductivity. This analysis helps draw a picture of the relationship between membrane morphology and dynamics of PFSA membranes.

Rheological properties of enzymatic milk gel: Effect of ion partitioning in casein micelles

Casein micelles (CMs) are colloids of ∼150 nm diameter formed by the association of milk proteins and minerals. Divalent milk cations, i.e. Ca 2+ and Mg 2+ , exist in two forms in CMs: either directly bound to casein residues (C-bound) without inorganic phosphate, or in a precipitated form called micellar calcium phosphate (MCP). The composition and properties of CMs vary with changes of the physicochemical conditions of milk; e.g. after the addition of salt or a change of pH. Moreover, the rheological properties of enzymatic milk gels are known to be strongly influenced by variations of mineral equilibria. We report in this study on the effect of cation partitioning in CMs on the rheology of enzymatic milk gel. Firstly, salts and acid (CaCl 2 , MgCl 2 , Na 2 HPO 4 , Na 3 Cit and HCl) were added to produce a set of 19 milk samples containing different proportions of C-bound and MCP in order to identify correlations with rheological parameters (G′, G″, tanδ) of the resulting gels. Three milks were then selected according to the mineral content of CMs and the resulting gels were further characterized in order to propose mechanisms that might explain the dependence of gel macroscopic properties on those of CMs. We showed that the rheological properties of gel were well correlated with the two types of cations present in CMs: an increase in C-bound cations raised the values of G′ and G″ while an increase in the MCP content lowered the tanδ. To explain these inter-dependencies, CMs were viewed as soft colloids whose modulus could be tuned by their MCP content. Consequently, CMs with different mineral contents would have differing abilities to fuse after aggregation, which appeared to link the rheological and microscopic attributes of the gels in a consistent manner. These results will be useful to understand the complex variations in the rheological properties of milk gels produced in the dairy industry. • Micellar cations exist as directly bound to casein (C-bound) or as MCP. • G′ and G″ of enzymatic milk gel are positively correlated to C-bound. • tanδ is negatively correlated to MCP. • Kinetics of gel aging depends on the MCP and on the rate of fusion of para-micelles.

Ion Partition Detected in Homeopathically Manufactured Medicine Cuprum metallicum and Controls

Background: Homeopathy is highly controversial. The main reason for this is its use of very highly dilute medicines (high homeopathic potencies, HHP), diluted beyond the Avogadro/Loschmidt limit. Research using Nano Tracking Analysis has demonstrated the presence of particles in HHPs. This study aims to verify the results of a previous publication that identified the ionic composition of these particles in all dilutions.
 Methods: We used Scanning Electron Microscopy & Energy Dispersive X-Ray Spectroscopy (SEM-EDX) to examine dilutions of a commonly used homeopathic medicine, an insoluble metal, Cuprum metallicum, for the presence of particles (NPs). The homeopathic medicines tested were specially prepared according to the European pharmacopoeia standards. We compared the homeopathic dilutions/dynamizations of copper with simple dilutions and dynamized lactose controls.
 Results: We observed an ionic diversity common to all preparations including HHPs but also significant differences in the relative quantity of each ion between manufacturing lines of homeopathic copper and lactose controls. The probability that the observed differences could have occurred chance alone (especially above Avogadro limit) can be rejected at p < 0.001. The essential component of these homeopathic medicines is sodium hydrogen carbonate, modulated by some other elements and by its quantity, size and shape.
 Conclusion: Homeopathic medicines made of Cuprum metallicum do contain material with a specific ionic composition even in HHPs diluted beyond the Avogadro/Loschmidt limit. This specificity can be attributed to the manufacturing process. This material demonstrates that the step-by-step process (dynamized or not) does not match the theoretical expectations of a dilution process. The starting material and dilution/dynamization method influences the nature of these NPs. Further measurements are needed on other raw materials using the same controls (solvent and simply diluted manufacturing lines) to support these findings. The role of sodium bicarbonate must be carefully studied in the future.

Ion partitioning and ion size effects on streaming field and energy conversion efficiency in a soft nanochannel

Ion partitioning and ion size effects on streaming field and energy conversion efficiency in a soft nanochannel

Integrated Approach to Extract and Purify Proteins from Honey by Ionic Liquid-Based Three-Phase Partitioning.

The purification of value-added compounds by three-phase partitioning (TPP) is a promising alternative to conventional processes since the target compound can be easily recovered from the liquid-liquid interphase. Although this technique has been successfully applied to the recovery of proteins, the minimization of the use of salts and solvents must be pursued to improve the overall process sustainability. Accordingly, we have here investigated the use of biobased glycine-betaine ionic liquids (IL) directly with honey, a carbohydrate-rich matrix, as phase-forming components of TPP systems. These ILTPP systems were applied in the purification of major royal jelly proteins (MRJPs) from honey. The results obtained show that MRJPs mostly precipitate in the ILTPP interphase, with a recovery yield ranging between 82.8% and 97.3%. In particular, MRJP1 can be obtained with a purity level up to 90.1%. Furthermore, these systems allow the simultaneous separation of antioxidants and carbohydrates to different liquid phases. The proposed approach allows the separation of proteins, antioxidants, and carbohydrates from honey in a single step, while using only ILs and a real carbohydrate-rich matrix, thus being sustainable TPP processes.

New insights into Mn2+ and Mg2+ inhibition of calcite growth

Impurity ion and isotope partitioning into carbonate minerals provide a window into the molecular processes occurring at the fluid-mineral interface during crystal growth. Here, we employ calcium isotope fractionation together with process-based modeling to elucidate the mechanisms by which two divalent cations with starkly contrasting compatibility, magnesium and manganese, inhibit calcite growth and incorporate into the mineral lattice. Calcite growth inhibition by Mg2+ is log-linear and KMg is on the order of 0.02–0.03 throughout the range of {Mg2+}/{Ca2+} studied here (0.01–2.6). Mn2+ exhibits much stronger log-linear growth rate inhibition at low Mn2+ concentrations (fluid {Mn2+}/{Ca2+} = 0.001–0.02). Mn2+ is readily incorporated into the calcite lattice to form a calcite-rhodochrosite solid solution, with large partition coefficients (KMn 4.6–15.6) inversely correlated to growth rate. For both Mn2+ and Mg2+, calcium isotope fractionation is found to be invariant with {Me2+}/{Ca2+} despite more than an order of magnitude decline in growth rate. This invariant Δ44/40Ca suggests that the presence of Mn2+ or Mg2+ does not significantly change the relative rates of Ca2+ attachment and detachment at kink sites during growth, indicative of a dominantly kink blocking inhibition mechanism. Because the partitioning behavior dictates that Mn2+ must attach to the surface significantly faster than Ca2+, attachment of Mn2+ is likely to be as a non-monomer species such as an ion pair or possibly a larger polynuclear cluster. We propose that calcite growth rate inhibition by Mn is determined by the kinetics of carbonate attachment at Mn-occupied kink sites, potentially due to slow re-orientation kinetics of carbonate ions that have formed an inner-sphere complex with Mn2+ at the surface but must reorient to incorporate into the lattice. We demonstrate that patterns in Mg2+ partitioning and inhibition behavior are broadly consistent with growth inhibition driven by slow Mg2+-aquo complex dehydration relative to Ca2+ but argue that this mechanism likely represents one endmember scenario, seen in Mg-calcite growth at low supersaturations and net precipitation rates. During growth at faster net precipitation rates, some portion of Mg2+ is likely incorporated as a partially hydrated or otherwise complexed species, but calcite growth remains significantly inhibited by the kinetics of CO32− attachment at Mg2+ kink sites. These findings suggest a hybrid classical/nonclassical growth mechanism whereby Ca2+ incorporates largely as a free ion at kink sites while Mn2+ and some portion of Mg2+ are incorporated via non-monomer attachment. This pattern may be generalizable; trace constituent cations with aquo-complex desolvation rates significantly slower than the mineral growth rate preferentially incorporate as a non-monomer species during otherwise classical crystal growth.